In the new study, Destounis and her colleagues evaluated records of all mammograms conducted at the imaging center from 2000 to 2010. They focused on 373 women in their 40s diagnosed with breast cancer after a routine mammogram. Of these, 228 -- or 61 percent -- had no family history of the disease. Seventeen were excluded because of a personal history of cancer or other high-risk status.
Of the 211 women remaining, nearly 64 percent had invasive disease, and 15 percent had cancer cells in their lymph nodes.
"This study reinforces the importance of screening mammography in the 40-to-49 age group with no family history as a risk factor," Destounis concluded.
However, the chair of the USPSTF said the study does not prove that the cancers were detected because of the mammograms.
"The assumption is made that these women did better because invasive cancers were found by screening," said Dr. Virginia Moyer, also a professor of pediatrics at Baylor College of Medicine in Houston. "The only way to know that is to randomize [women] to screening or not." That would mean assigning one group of women to screening and another to no screening.
Those are the kinds of studies the task force looked at when producing the 2009 guidelines, Moyer said. The USPSTF found a small benefit for women in their 40s balanced by a moderate risk of harms, she said.
"Their data only shows they found invasive cancer, not that the women benefited directly from the mammogram," Moyer added.
Data and conclusions of research presented at medical meetings should be considered preliminary until published in a peer-reviewed medical journal.
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